Alex Turner takes the award for the Arctic Monkeys, whose refusal to play the media game has irked some critics. Photograph: Stephen Hird/Reuters

The Nationwide Mercury prize judges sprung a surprise last night by anointing the runaway favourites as winners.

Arctic Monkeys capped a year in which they released the fastest selling debut ever, reinvigorated the music industry and lost a founder member, by winning the annual prize which is designed to reward the best release of the year regardless of genre or sales.

The Sheffield four-piece, whose mixture of classic guitar melodies and acutely observed lyrics garnered critical and commercial acclaim, won the prize for Whatever People Say I Am, That's What I'm Not.

"Normally it doesn't go to a band who has sold as many records as we have," said frontman Alex Turner as he collected the award, referring to the judges' tradition of opting for leftfield winners.

"We're pleased with it. Good tunes is what we try to do and no tricks, really. There's too many people trying to do too many tricks," he added.

This time last year the band were yet to release their first full single, the number one hit I Bet You Look Good on the Dance Floor, but had already built up a big live following after fans swapped their demos online.

Last night the band attempted to distance themselves from the myth that has built up around the role of the web in their rise to fame. Following a second number one single, When the Sun Goes Down, their album sold 363,000 copies in its first week on sale alone. Turner, whose witty lyrics have been compared to Pulp's Jarvis Cocker and Mike Skinner of The Streets, said fellow Sheffield artist Richard Hawley should have won. "Someone call 999, Richard Hawley's been robbed," he quipped on taking the stage to collect the £20,000 prize.

But their rise has not been without its casualties. Bassist Andy Nicholson was recently replaced by Nick O'Malley after pleading fatigue and some critics have accused them of running out of momentum and taking an overly taciturn stance to fans and the media. They anticipated the backlash in April with the release of an EP entitled Who the Fuck Are Arctic Monkeys? that was deliberately ineligible for the charts.

Last night they said they were happy to win but less than happy at having to face the media afterwards. As guitarist Jamie Cook glared, drummer Matt Helders responded to claims that they had failed to play the game. "We've been doing a social experiment to see if we had to do it or not. And we didn't," he said.

Earlier this year they didn't show up for the Brit awards and their refusal to appear on Top of the Pops was widely interpreted as the final nail in the venerable BBC show's coffin.

The rapper Sway, nominated for self-produced debut This is My Demo, said he thought the award should have gone elsewhere. "Arctic Monkeys have been a phenomenal story this year but I didn't expect it to go to them because they have been so successful already," he said. "I thought they would go for a more creative choice. If I had lost out to Hot Chip I would have understood a lot more."

Given Arctic Monkeys' already impressive sales, others are likely to benefit more from the increased exposure afforded by a place on the list of 12 nominees and the attendant radio and television coverage.

Since its inception in 1992 the prize, designed to reward British musical creativity rather than record sales, has each year seen an increase in its effect on boosting the profile of nominated artists. Before her nomination, avant-garde jazz pianist Zoe Rahman had sold 700 copies of her album Melting Pot. But according to figures provided by online store Amazon, Rahman has seen a 938% increase in sales since her nomination was announced last month.

But it was Sheffield crooner Hawley, who has been called a Yorkshire Johnny Cash, who is being tipped to hit the mainstream with his nominated Coles Corner. HMV said Hawley had enjoyed the biggest rise in sales in its stores, with a 336% increase since being nominated.

"Nominated artists can stand to gain massively from the halo effect of being in the Mercury's spotlight, which will not only boost sales of their albums, but can act as a catalyst in their careers,"said Gennaro Castaldo of HMV. He said it was "the slightly less high profile, but no less credible acts" such as Hawley, Guillemots, Hot Chip and Editors who stood to gain most out of being nominated.

Antony and the Johnsons saw their sales rise five-fold after winning the prize last year. Matt Henderson, senior music product manager at Amazon, said the award had risen in relevance as music fans had become more eclectic.